When a subscriber terminal moves, measures must be taken which make sure that the subscriber terminal always listens to the base station that is best heard. The subscriber terminal receives system information sent by the base station on a control channel informing which neighbour base stations the subscriber terminal should also listen to. When the subscriber terminal detects that the received power of a neighbour cell signal it has listened to and possibly some other parameters are better than that of the cell, whose control channel the subscriber terminal has been listening to, then the subscriber terminal decides to perfrom cell re-selection. A network part of a cellular network, i.e. the network infrastructure including, for example, base stations, base station controllers and mobile services switching centres, can also discover the need for cell re-selection and inform the subscriber terminal about it. In connection with cell re-selection the subscriber terminal has to receive the system information of a new cell sent on its control channel.
In an ordinary GSM system the system information has a standard structure. In a cellular network using GPRS the structure and length of the system information sent by different cells may vary a lot. The subscriber terminal does not know in advance how long it takes to read the system information. In demanding packet transmission applications this may result in a situation, where a fairly long break may occur in performing packet transmission so that the user detects the break as a delay in the application operation. The user may interpret the delay as poor quality service.